As is known, part of the research carried out in the tyre industry is centred around improving tread wear resistance.
For this purpose, silica has long been used as a reinforcing filler in tread compounds, as a partial or total substitute for carbon black, because of the advantages it affords in terms of rolling resistance and wet road-holding performance.
Silica is used in combination with silane coupling agents, which bond with silanol groups to prevent the formation of hydrogen bonds between silica particles, and at the same time bond the silica chemically to the polymer base.
Using large-area silica in rubber compounds has been found to greatly improve the wear resistance of the compound.
Another ingredient found to improve the wear resistance of rubber compounds is a particular S-SBR polymer mix, which is characterized by containing 25-45% styrene and 20-70% vinyl, and by comprising 10-90% of a first fraction with a mean molecular weight of 50-100×103 and a molecular weight distribution of ≦1.5 , and 10-90% of a second fraction with a mean molecular weight of 800-1500×103 and a molecular weight distribution of ≦3.0.
Both large-area silica and the above polymer mix, however, have the drawback of excessively increasing the viscosity of the mix, which obviously poses processing problems, not least of which are higher mixing power consumption and heating of the mix itself.
A need is therefore felt for a method of producing tread compounds, which enables the use of at least large-area silica, without impairing the workability of the mix.
The Applicant has surprisingly devised a method of producing tread compounds, designed to meet this demand.